Ecology and Demography of Free-Roaming Domestic Dogs in Rural Villages near Serengeti National Park in Tanzania

<div><p>Free-roaming dogs (<i>Canis lupus familiaris</i>) are of public health and conservation concern because of their potential to transmit diseases, such as rabies, to both people and wildlife. Understanding domestic dog population dynamics and how they could potentially be impacted by interventions, such as rabies vaccination, is vital for such disease control efforts. For four years, we measured demographic data on 2,649 free-roaming domestic dogs in four rural villages in Tanzania: two villages with and two without a rabies vaccination campaign. We examined the effects of body condition, sex, age and village on survivorship and reproduction. Furthermore, we compared sources of mortality among villages. We found that adult dogs (>12mos) had higher survival than puppies in all villages. We observed a male-biased sex ratio across all age classes. Overall survival in one non-vaccination village was lower than in the other three villages, all of which had similar survival probabilities. In all villages, dogs in poor body condition had lower survival than dogs in ideal body condition. Sickness and spotted hyena (<i>Crocuta crocuta</i>) predation were the two main causes of dog death. Within vaccination villages, vaccinated dogs had higher survivorship than unvaccinated dogs. Dog population growth, however, was similar in all the villages suggesting village characteristics and ownership practices likely have a greater impact on overall dog population dynamics than vaccination. Free-roaming domestic dogs in rural communities exist in the context of their human owners as well as the surrounding wildlife. Our results did not reveal a clear effect of vaccination programs on domestic dog population dynamics. An investigation of the role of dogs and their care within these communities could provide additional insight for planning and implementing rabies control measures such as mass dog vaccination.</p></div

Hazard ratios, standard errors, 95% confidence intervals and <i>p</i>-value results of multivariable adjusted Cox proportional hazards model comparing the risk of death across villages, age categories, BCS, sex, reproduction, and vaccination status.

<p>Hazard ratios, standard errors, 95% confidence intervals and <i>p</i>-value results of multivariable adjusted Cox proportional hazards model comparing the risk of death across villages, age categories, BCS, sex, reproduction, and vaccination status.</p

Total number of dogs recorded each year of the study in each village census.

<p>The blue line represents the non-vaccination villages (Buyubi and Iyogelo) and the red line represents the vaccination villages (Nangale and Sanungu). The trendline indicates the mean predicted instantaneous rate of increase (r = 0.08 per year) between 2010 and 2013 in all villages.</p

Kaplan-Meier survival estimates indicating the probability of a dog surviving until the next year of observation after it was first encountered.

<p>Dogs in Iyogelo village (non-vaccination, indicated by solid blue line) had lower survival probabilities compared to dogs in Buyubi (non-vaccination, blue dashed line), Nangale and Sanungu (vaccination, red dotted line and dash-dot respectively) throughout the study period. The x-axis (analysis time) indicates the year of observation after a dog was enrolled into the study and the y-axis indicates the survival probability.</p

Percentage of body condition scores (BCS) of dogs alive in 2013.

<p>Blue bars represent non-vaccination villages (Buyubi and Iyogelo). Red bars represent vaccination villages (Nangale and Sanungu). Body condition was scored as 1–2 = poor; 5 = ideal; 8–9 = obese. We did not observe any obese dogs throughout the study. Error bars indicate 95% confidence intervals.</p

Percentage of owner-reported causes of death of dogs enrolled in the study.

<p>Blue bars represent non-vaccination villages (Buyubi and Iyogelo). Red bars represent vaccination villages (Nangale and Sanungu). Error bars represent 95% confidence intervals.</p

Summary statistics of GLM best model assessing effects of village and year on the total number of dogs.

<p>Summary statistics of GLM best model assessing effects of village and year on the total number of dogs.</p

Study cohort, village dog and human population census totals and estimated growth rates 2010–2013.

<p>Study cohort, village dog and human population census totals and estimated growth rates 2010–2013.</p

Percentage of litters of puppies born (<i>n</i> = 716) throughout the study in each month of the year.

<p>Lighter colored bars (March-May and November-December) indicate typical rainy season conditions. Dark colored bars (January-February and June-October) indicate typical dry season. Error bars represent 95% confidence intervals.</p

Sources for Eastern Massasauga life history information including locality and study years.

<p>Sources for Eastern Massasauga life history information including locality and study years.</p